title: Knockdown and larvicidal activity of six monoterpenes against Aedes aegypti (Diptera: Culicidae) and their structure-activity relationships.
abstract: The relationships between physicochemical parameters of majority components of Eucalyptus essential oils and their insecticide effect were evaluated on Aedes aegypti (L.) (Diptera: Culicidae). The octanol-water partition coefficients of the monoterpenes were estimated by the atom/fragment contribution method and the vapor pressures were determined by our laboratory in previous studies. The larvicidal activity (LC50 (ppm)) and knockdown effect (KT50 (min)) of each component was determined. The results show that the toxicity of EOs main components of Eucalyptus on adults and larvae of A. aegypti is strongly related to their physicochemical properties (vapor pressure and Log P). However, the interaction of both variables (vapor pressure * Log P) explains the toxicological phenomenon more precisely. The regression models were expressed as follows: KT 50(min) =  - 10.9 + 3.7 * Log P + 1.9 * 1/Pvapor (R(2) = 0.80; F = 42.5) and LC 50(ppm) =  - 94.3 + 438.6 *  1/Log P + 2.8 *  1/Pvapor (F = 57.8; R(2) = 0.85). The six evaluated components present different functional groups. Therefore, it was considered to evaluate the monoterpenes as a group and separated in two groups: oxygenated monoterpenes (α-terpineol, 4-terpineol, and 1,8-cineole) and terpene hydrocarbons (γ-terpinene, p-cymene, and α-pinene). The results show the regression models for each group as follows: (A) oxygenated terpenes: KT 50(min) = - 515.3 + 1613.2 * 1/Log P + 5, 2 * 1/Pvapor (F = 3176.7 R(2) = 0.99) and LC 50(ppm)  =  - 1679.4 + 5402.1 * 1/Log P + 12.7 *  1/Pvapor (F = 282.9; R(2) = 0.99). (B) Hydrocarbons terpenes: KT 50(min) = 18.2 - 58.3 * 1/Log P + 2.7 * 1/Pvapor (F = 171.7;  R(2) = 0.97) and LC 50(ppm) = - 21.1 + 174.9 * 1/Log P - 14.3 * 1/Pvapor (F = 410.0; R(2) = 0.99). The association between the toxic effect of the evaluated monoterpenes against A. aegypti and the physicochemical properties can be better described when they are separated into functional groups (hydrocarbons vs. oxygenated terpenes).
authors.affiliation: Centro de Investigaciones de Plagas e Insecticidas (CIPEIN) (UNIDEF (MINDEF-CONICET), Juan Bautista de La Salle 4397, 1603, Buenos Aires Province, Villa Martelli, Argentina, luciaalejandro@yahoo.com.ar.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Lucia
authors.forename: Eduardo
authors.initials: E
authors.lastname: Zerba
authors.forename: Hector
authors.initials: H
authors.lastname: Masuh
mesh_terms: D000330:Aedes / Q000187:drug effects*; D000818:Animals; D000081008:Bicyclic Monoterpenes; D000081005:Cyclohexane Monoterpenes; D003511:Cyclohexanols; D053138:Cyclohexenes; D000081007:Cymenes; D000077591:Eucalyptol; D005052:Eucalyptus / Q000737:chemistry*; D007306:Insecticides / Q000737:chemistry*; D007814:Larva / Q000187:drug effects; D039821:Monoterpenes; D009032:Mosquito Control; D009822:Oils, Volatile / Q000737:chemistry*; D013329:Structure-Activity Relationship
chemical_list: D000081008:Bicyclic Monoterpenes; D000081005:Cyclohexane Monoterpenes; D003511:Cyclohexanols; D053138:Cyclohexenes; D000081007:Cymenes; D007306:Insecticides; D039821:Monoterpenes; D009822:Oils, Volatile; C007210:4-cymene; C016775:alpha-terpineol; C018669:gamma-terpinene; C005451:alpha-pinene; D000077591:Eucalyptol